OIL IN RADIATOR HEADER TANK.

1998 Vauxhall Sintra

Engine Mechanical problem
1998 Vauxhall Sintra Manual

when I started driving there was a knocking/ticking noise coming from the engine (sounded like playing card in bycicle wheel). However it only knocked when the accellerator pedal was depressed. I drove like this for a few miles before there was a lack of power. The temperature started to climb then the engine died. When the bonnet was lifted there was steam coming from the header tank and it was full of oil. There is no water in the head. Oil filler cap clean, no white gunk. Help.